For about thirty years, chemically treated sheet materials have been used in one way or another to protect metal surfaces against corrosion and for this purpose corrosion inhibiting material has generally been a composition which works by releasing a vapor which engages the metal surface and inhibits the corrosion effect of any moisture vapor that may be in the surrounding air. Various corrosion inhibiting compositions have been employed successfully and apparently each manufacturer of a product for this use has his own formulation and manner of application. Almost all, however, have settled upon an inhibitor loading factor of about 10 to 20 pounds, dried weight, per 3,000 square feet of the treated sheet material, or, expressed in another way, about 1.512 to 3.024 grams per square foot. The inhibiting material is applied to the substrate in various ways such as coating, spraying, saturating, or by printing, such as is described in U.S. Pat. Nos. 2,739,872 and 3,007,767. Recently the U.S. Department of the Navy MIL P-3420 Qualifying Test Program has listed as acceptable Type I, Class 3, Style A corrosion inhibitor sheet material for medium duty service, products of various manufacturers carrying corrosion inhibitor compositions in amounts ranging from about 1.512 to 3.024 grams, dry weight, per square foot of sheet area.
The research department of applicant's company developed a ferrous metal corrosion inhibitor consisting of 15 parts Urea, 15 parts Sodium Nitrite, 10 parts Sodium Benzoate and 60 parts water which, when used in the conventional loading of 3.024 grams per square foot on 40 pound natural kraft, was found to pass all qualifying tests of the Department of the Navy and is listed on the MIL 3420E Qualified Product List as a Type I, Class 3, Style A corrosion inhibitor.
In connection with efforts to determine how the vapors of conventional vapor phase inhibitors (VCI) function to prevent oxidation of ferrous metal surfaces, applicant suggested that the new corrosion inhibitor composition be tested in the usual manner with 40 pound kraft spaced area--printed with a loading of only 10% to 20% of the conventional loading amount. Accordingly a production run of material as so specified was made and successive in-house corrosion inhibition tests appeared to be so successful that this material, which was determined to have an inhibitor load factor of 0.272 grams per square foot, was submitted to a professional testing laboratory and to the U.S. Navy Department for testing according to military standards and each of these organizations found that this new product passed all MIL P-3420 Qualifying Tests. As a result, this new product is now listed as a MIL P-3420 E Type I, Class 3, Style A corrosion inhibitor.
In view of the foregoing statement, it is believed that applicant's off-hand suggestion has resulted in a discovery that is a material advance in this already crowded art, particularly in that the new product results in a considerable saving of cost in the manufacture of ferrous metal corrosion inhibiting products.